A: Infrared Absorption á197Mñ.

B: Ultraviolet Absorption á197Uñ—

C: To 5mLof a solution (1in 100)add 1mLof bromine water TS:the bromine color is discharged.

Isopropyl alcohol solution— Dilute 295mLof isopropyl alcohol with water to 500mL.

Buffer solution— To 55g of sodium chloride in a 1-Lvolumetric flask add 500mg of sodium citrate,255g of sodium acetate,and 300mLof water.Shake to dissolve,and add 115mLof glacial acetic acid.Cool to room temperature,add 300mLof isopropyl alcohol,dilute with water to volume,and mix.The pHof the resulting solution is between 5.0and 5.5.

Reagent blank— Pipet 15mLof 1,2-dimethoxyethane into a flat-bottom,glass-joint,500-mLflask,and proceed as directed for Test stock solution,beginning with “add the contents of a 15-mLvial of sodium biphenyl solution.”

Modified calomel reference electrode— Mix 70mLof a freshly prepared saturated potassium chloride solution with 30mLof isopropyl alcohol,fill the electrode with the clear supernatant,and allow the electrode to soak in the remainder of the solution for a minimum of 2hours before using.Store the electrode immersed in the potassium chloride-isopropyl alcohol solution when not in use.

Standard stock solution— Accurately weigh 2.211g of sodium fluoride,previously dried at 150for 4hours,transfer to a 1-Lvolumetric flask,and dissolve in about 200mLof water.Add 1mLof sodium hydroxide solution (1in 25),dilute with water to volume,and mix.Store this solution in plastic containers.One mLis equivalent to 1mg of fluoride.

Standard curve— Dilute 10.0mLof Standard stock solutionwith water to 100mL.Into each of four 100-mLvolumetric flasks,pipet 0.8,1.0,1.2,and 1.6mL,respectively,of the resulting solution.To each flask add 15mLof Reagent blank,dilute with Buffer solutionto volume,and mix.Use these dilutions,containing,respectively,0.8,1.0,1.2,and 1.6µg per mL,to construct the standard curve as follows.Determine the potentials of each solution as directed for Procedure.Plot the results of fluorine concentration,as the abscissa,in mg per 100mLversus the potential,as the ordinate,on semilogarithmic graph paper,for each of the standards.Draw the best straight line through the plotted points.

Test stock solution— Place 200mg of Fluorouracil,accurately weighed,in a 250-mLvolumetric flask,add about 150mLof 1,2-dimethoxyethane,shake by mechanical means to dissolve,dilute with the same solvent to volume,and mix.Pipet 15mLof this solution into a flat-bottom,glass-joint,500-mLflask,add the contents of a 15-mLvial of sodium biphenyl solution through a long-stem funnel to prevent splattering,swirl the flask gently,and cover with a watch crystal.Allow to stand at room temperature for 20minutes,then cautiously add 50.0mLof isopropyl alcohol while swirling the flask.Add 10.0mLof 30percent hydrogen peroxide and 4.0mLof 1Nsodium hydroxide,and connect the flask to a water-cooled reflux condenser that has previously been cleaned with water and isopropyl alcohol and dried.Place the flask on a hot plate,set at about 245,and reflux for 1hour.Cool to room temperature,rinse the condenser with 15mLof Isopropyl alcohol solution,transfer the contents of the flask to a 250-mLvolumetric flask using Isopropyl alcohol solutionas a rinse,dilute with the same solvent to volume,and mix.

Test solution— Pipet 15mLof the Test stock solutioninto a 100-mLvolumetric flask,and dilute with Buffer solutionto volume.

Procedure— Measure the potential,in mV,of the Test solution,with a suitable pHmeter having a minimum reproducibility of ±0.2mV,and equipped with a fluoride-specific ion electrode and a glass-sleeved Modified calomel reference electrode.When taking a measurement,immerse the electrodes into the solution,which has been transferred to a 150-mLplastic beaker,insert a suitable plastic-coated stirring bar,place the beaker on a magnetic stirrer,taking adequate precautions to prevent heat transfer,and stir for 2minutes before reading.Dry the electrodes between measurements,taking care not to scratch the crystal surface of the specific ion electrode.Determine the quantity of fluorine,in mg per 100mLof the Test solution,from the Standard curve.Multiply the quantity by the factor 138.9to express the result as a percentage:not less than 13.9%and not more than 15.0%of fluorine,calculated on the dried basis,is found.

Mobile phase— Use degassed and filtered water.

Standard preparation— Dissolve an accurately weighed quantity of USP Fluorouracil RSin water,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 10µg per mL.

Assay preparation— Transfer an accurately weighed quantity of about 20mg of Fluorouracil to a 200-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Quantitatively dilute a known volume of this solution with water to obtain a solution having a concentration of about 10µg per mL.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×30-cm column containing packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency is not less than 2500theoretical plates,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C4H3FN2O2in the portion of Fluorouracil taken by the formula: in which Cis the concentration,in µg per mL,of USP Fluorouracil RSin the Standard preparation;and rUand rSare the fluorouracil peak responses obtained from the Assay preparationand the Standard preparation,respectively.